Download PCL Injury Part 1

 QUESTION | MY PATIENT HAS A PCL INJURY BUT HAS BEEN TOLD HE DOES NOT NEED
AN OPERATION. WHAT MAKES THE PCL SO DIFFERENT FROM THE ACL?
In this month's Question for Physiotherapists, Dr Doron Sher discusses PCL injury. Part one of
a two part series - this article will focus on the anatomy, biomechanics and function of the PCL
and an injury classification system. Next month will look at examination, investigations and
treatment.
ANSWER | PCL injuries can be very roughly divided into low energy and high energy injuries. This makes it
very difficult to generalize when it comes to treatment since the two groups are so different. Low
energy sporting injuries to the PCL account for about 3% of all knee injuries and this article will
focus on these patients (Up to 1/3 of multi-trauma patients with injuries to their knees also injure
their PCL and other structures). There have been major advances recently with regards to the
anatomy and biomechanics of the PCL but the improvements in clinical outcomes have not
been as impressive. Many studies have looked at inlay fixation rather than tunnel fixation, single
and double bundles, the femoral tunnel locations and graft tensioning. No single reconstructive
technique has yet been shown to be superior to the others but we do know that addressing the
PCL without fixing a posterolateral corner injury (if there is one present) will lead to inferior
results.
Anatomy
The PCL is the primary restraint to posterior translocation of the proximal tibia and is a
secondary restraint to varus, valgus, and external rotation forces. It originates from a broad,
crescent-shaped area on the anterolateral aspect of the medial femoral condyle in the
intercondylar notch and inserts into a depression between the two tibial plateaus named the
PCL fossa. The PCL has a wide variation in shape and size of its femoral attachments, whereas
the tibial attachment patterns are fairly constant. It is extra-articular and lies within its own
synovial sheath.
The PCL is 32 to 38 mm long, with a cross-sectional area of 11 mm2 at its midpoint. The
midsubstance of the ligament is approximately one third the diameter of both the femoral and
tibial insertion sites. The PCL complex includes the anterior (ligament of Humphrey), and
posterior (ligament of Wrisberg) meniscofemoral ligaments. It is known that the meniscofemoral
ligaments contribute to posterior drawer stability. There are no attachments between the PCL
and the medial meniscus.
The PCL can be functionally divided into two components: a larger anterolateral (AL) bundle
and a smaller posteromedial (PM) bundle. This terminology is derived from the relationship of
the anatomic location of the femoral insertion (anterior or posterior) to the tibial insertion (lateral
or medial). These bundles have different functions that allow the PCL to resist posterior
translation in both extension and flexion. The AnteroLateral Bundle makes up the bulk of the
ligament and is taut at 90 degrees of flexion and loose in extension, whereas the PosteroMedial
Bundle is taut at 30 degrees of flexion and loose at 90 degrees of flexion. This makes the PCL a
complex, anisometric continuum of fibers whose patterns of orientation and tension differ with
differing knee flexion angles.
The PCL is the primary restraint to posterior tibial translation at all flexion angles greater than 30
degrees and is a secondary restraint to external rotation of the tibia. Posterior knee structures
provide the primary restraint from 0 to 30 degrees. These are the: posteromedial and
posterolateral capsule, medial collateral ligament (MCL), lateral collateral ligament (LCL),
arcuate, meniscofemoral; and fabellofibular ligaments. The PCL provides increasing resistance
to posterior translation from 30 to 90 degrees of knee flexion. At 90 degrees it provides 95% of
the total restraining force for the straight posterior drawer. Both bundles of the PCL play an
important role during posterior tibial loading. As the knee progresses from flexion to extension,
the tibia externally rotates relative to the femur (Traditionally called the "screw-home"
mechanism of the knee). This mechanism is related to a combination of factors including the
bony anatomy of the knee and the relative lengths of the cruciates.
Blood Supply
The majority of the blood supply to the PCL stems from the middle genicular artery, a branch of
the popliteal artery. The middle genicular artery also supplies the synovial sheath, which itself is
a major contributor to the blood supply of the PCL.
Nerve Supply
The PCL and its synovial sleeve are supplied by nerve fibers from the popliteal plexus. The
popliteal plexus is derived from the posterior articular nerve and the terminal branches of the
obturator nerve. Injury to the PCL not only creates a mechanical disturbance but also a
neurologic one by disrupting the afferent signals to the central nervous system.
Biomechanics
It was initially thought that conservative treatment of isolated PCL injuries had good results.
Newer studies are questioning this because they have shown higher rates of arthrosis
developing many years later. This has led to
an increased interest in the surgical reconstruction of PCL injuries. Research done on the
biomechanics of the PCL has allowed an evolution in surgical techniques for PCL
reconstruction. These biomechanical studies have shown that the joint contact force in the
medial femoral condyle increases by up to 34% under combined posterior tibial and axial loads
when the PCL is torn. There is no increase in the forces experienced in the menisci or lateral
articular compartment. This supports the role of the PCL as a secondary stabilizer to external
rotation and varus stress. Cutting the posterolateral corner (PLC) increases in situ -forces in the
PCL by 2 to 6 times compared with that of an intact knee. This is significant because PLC
injuries occur in many PCL injuries, and unrecognized injuries to the PLC make a PCL
reconstruction more likely to fail.
Mechanism of PCL Injury
PCL tears may result from a variety of injuries. Isolated injuries are usually from hyperflexion but
overall the majority of these injuries are caused by a posteriorly directed force on the proximal
tibia (Like a "dashboard" injury with the knee flexed or a fall onto a flexed knee with the foot in a
plantar-flexed position). These injuries commonly result in partial tears of the PCL with the PMB
remaining intact.
Injury patterns involving hyperextension, forced varus or valgus, and knee dislocations are
associated with PCL tears plus other ligament and vascular or nerve injuries.
Classification of PCL Injuries
PCL injuries are graded based on (1) Severity, (2) Time since injury, and (3) Presence of
associated injuries.
1) SEVERITY: Tears are graded I to III based on the degree of posterior tibial translation
compared with that of the contralateral leg. The medial tibial plateau usually sits 1 mm
anterior to the medial femoral condyle with the knee flexed to 90 degrees. Grade I tears
have 1 to 5 mm of excess posterior translation, but the anterior step-off is maintained.
Grade II tears have 5 to 10 mm of excess translation, which allows the medial tibial
plateau to become flush with the medial femoral condyle. Grade III injures have greater
than 10 mm of excess posterior tibial translation. This is best felt with the thumb moving
up and down over the medial joint margin.
Grade I and II injuries represent partial tears of the PCL, whereas grade III tears
represent complete tears and suspicion of associated injuries should be increased.
2) TIMING: Acute vs chronic. Acute injury is defined as within 3 weeks of injury. Chronic
PCL injures have a higher incidence of pericapsular stretching which might affect the
choice of graft material.
3) ASSOCIATED INJURIES: Isolated vs multi-ligament injured knees is important for
treatment decisions. Isolated injuries to the PCL may have good results with
nonoperative treatment, whereas multi-ligament injured knees have better outcomes
with surgical intervention. Patients with multi-ligament injured knees must be closely
evaluated for injuries to vessels, nerves, and other structures because they are more
likely to have dislocated their knee.
Surgical intervention is recommended for the PCL/ PLC-deficient knee with >10 mm increased
posterior translation and about 15° of increased external rotation.
Diagnosis
PCL disruptions can be interstitial disruptions (midsubstance tears), bony avulsions from the
tibia or femur, or insertional disruptions. PCL injuries range from isolated partial tears to PCL
injuries associated with multi-ligament injured knees. As injury severity varies, so does the
patient's presenting complaint
Stay tuned next month for the continuation of this article
Dr Doron Sher
www.orthosports.com.au